What happened
On 16 September 2012, a Hawker Hunter T7, registration G-VETA, was performing a private flight when the pilot was notified by air traffic control that an object had fallen from the aircraft. The object was identified as the left inboard fuel drop tank. The detachment occurred during the landing rollout on Runway 26 at Cotswold Airport. Despite the loss of the tank, the pilot experienced no adverse handling characteristics and completed a gentle landing. The aircraft was met on the runway by a fire tender, though no fuel leaks or injuries were reported.
The investigation
An internal investigation by the aircraft operator focused on the electro-mechanical release unit (EMRU) and the pylon release housing (FRH). While a jettison system test using the original EMRU passed, the unit failed when subjected to heavy shaking and forward pressure, simulating landing forces. Swapping the EMRU from the right side to the left side did not resolve the issue, which ruled out the EMRU itself as the primary cause.
Investigators then examined the left pylon FRH and discovered insufficient clearance between the manual release plungers and the top of the FRH casing. This lack of clearance meant the internal latching mechanism could be triggered with very little movement. Furthermore, the investigation found that the left FRH had significantly less free play and travel compared to both the right-side unit and spare units. It was also noted that the aircraft was operating under a Permit-to-fly that did not include a specific Swiss modification designed to prevent such occurrences.
Findings
- The left inboard drop tank detached due to a combination of inadequate clearance and insufficient free play within the release housing.
- This mechanical configuration created a "hair trigger" effect, where the slight physical jolt of landing was enough to actuate the internal latching mechanism.
- The aircraft was operating under a UK Permit-to-fly standard that lacked a specific Swiss modification intended to secure the tanks.
- A previous incident involving a similar aircraft type in 2008 had suggested that landing forces could cause the jaws to open, though no mechanical fault was found in that instance.